Yes, the stereo does that. If I remember correctly, I think its called ASC.
And yes, you can control it, or even turn it off.
I can tell you just got your car, you haven't read the owners manual yet, huh?
i read the manual, but i never came across that. i guess thats what u get for skimming. come to think of it i do remember if u hit the tuning knob it asks if you want to turn it off.
Press and hold the right knob on your stereo. The first setting is "ALC" or something (stands for Automatic loudness control I think). If you don't want the music to get louder then turn it to the off or lower setting.